1. Field of the Invention
This invention relates to electronic devices, and particularly to systems and methods for cooling electronic devices using liquid mist distributed in a carrier gas mixture to enhance thermal conduction in the gap separating an electronic device from a heat sink.
2. Description of Background
During the normal operation of electronic devices, particularly integrated circuit devices, significant amounts of heat can be generated. Therefore, these devices are subjected to even higher power or heat generation during the test and burn-in process. This heat can be continuously removed to prevent the integrated circuit device from overheating and resulting in damage to the device and/or a reduction in operating performance. Cooling devices, such as heat sinks, generally have been used in conjunction with integrated circuit devices to avoid such overheating. For example, a passive heat sink in combination with a system fan has been employed as a relatively simple means for cooling integrated circuits. In recent years, however, the power of integrated circuit devices has increased exponentially, resulting in a significant increase in the amount of heat generated by those devices. Consequently, it has become extremely difficult to extract a sufficient amount of heat from those devices to prevent them from overheating during test and burn-in.
Current methods for cooling integrated circuit devices involve conducting heat from the microprocessor chip to a heat sink comprising metal and then radiating the heat into the air. The better the transfer of heat between the chip and the heat sink metal, the better is the cooling. Some processors are packaged with air cooled heat sinks attached to them directly, while others include a thermal interface material (TIM), such as a thin, soft layer of thermal paste or high thermal conductivity solder at the interface between the chip and the heat sink. In test and burn-in operations, removable solids, liquids, and gases with thermal conductivities higher than air, e.g., helium, are generally preferred. The TIM serves not only to transfer heat from the chip to the heat sink but also provides some degree of mechanical compliance to compensate for mechanical stresses between the chip and the heat sink such as dimensional changes driven by the high operating temperatures of the chip. The thermal resistance of current thermal pastes is unfortunately higher than desired. Thus, thermal pastes have been replaced with lower thermal resistance materials such as indium for field applications. Also, TIM's previously used for die test and burn-in operations, e.g., helium, have been replaced with propylene glycol, which has an even higher thermal conductivity. Unfortunately, propylene glycol (PG) or PG with water can cause corrosion to integrated circuit devices and also can lead to the build up of a contaminating residue that remains after testing.
Further, there is a continuing need to improve the reliability of integrated circuit devices, which is defined as the lifetime performance integrity of a device under normal operating conditions. Integrated circuit manufacturers usually test their products to predict the average lifetime thereof in a short time by subjecting them to accelerated tests. Such tests utilize tougher working conditions than normal, e.g., higher temperature, voltage, current, and/or pressure, to test the lifetime of devices in harsh conditions. The challenge as far as the cooling capability is concerned is that the TIM's functionality desirably facilitates such testing at higher power dissipation levels without compromising overall structural integrity. Moreover, die testing can require detachable (or removable by drying, evaporation, etc.) TIM materials that can be easily introduced at the beginning of the test and removed without any trace on the product after the testing.